In the power distribution industry, it is necessary to take care of challenges that are faced due to the modification, addition or removal of some components in the circuitry. Such is a device – a current limiting reactor that helps in reducing the available short circuit level to a value that is safe to use, matches with the rating of switchgear or fulfills other design requirements.
Generally, switchgear is only rated for a given value of short circuit current rating. However, situations may arise where short circuit current may flow above the rated capacity of switchgear. This is why a current limiting reactor is required for keeping the situation under control. There are generally three variants of current limiting reactors such as:
- Series Current Limiting Reactor
- Solid State Fault Current Limiters
- Superconducting Fault Current Limiters
Sometimes, current limiting fuses are used to limit the passing current in a way that they interrupt the short circuit current before quarter cycle of the short circuit current waveform.
Based on their construction, current limiting reactors are categorized into two types, named as:
- Air Core Reactor
- Iron Core Reactor
Though iron core reactors occupy an only small area, they can saturate when the value of short circuit current surges upward with a great difference. As a result, the effective impedance gets reduced. Thus, an iron core reactor is not considered as an ideal candidate for short circuit limiting applications. On the other hand, air core dry type reactors don’t come with such disadvantages and are basically used for applications that require short circuit current limiting.
Benefits of Air Core Reactors
- When high magnitude current flows through the reactor, there is no occurrence of saturation. However, its counterpart gets saturated in similar conditions.
- Dry type air core reactors are known for low losses (i.e. high IQ) and fewer maintenance requirements throughout their lifetime.
- They can be installed either vertically stacked or side by side; however necessary magnetic clearances recommended by the manufacturer are needed to be followed.
Drawbacks of Air Core Reactors
- Due to its basic nature, it produces more stray magnetic field when compared with an iron core reactor. While iron core reactor can confine the magnetic flux in its core, there is nothing to restrain the magnetic flux in an air core reactor.
- As there can be potential interaction between magnetic flux of different phases in a three-phase reactor stack, it is mandatory to follow the manufacturer’s recommended clearances. This implies that this type of reactor often occupies larger physical space.
- Additional personnel fencing installation may be required to prevent personnel exposure to high magnetic field.
- All of the equipment and sensitive electronics items that are susceptible to high magnetic field must be placed outside the boundary of magnetic field suggested by the manufacturer.
If precautions are taken and manufacturer’s recommendations are followed thoroughly, air core reactor is considered to be highly efficient in operation than its counterpart. Therefore, air core type current limiting reactors are more prevalent in the industry when compared with iron core reactors.